Naturally, I'd be disappointed, but on the other hand, if they aren't thieving crackheads who fenced VCRs to feed their habits (MST3K reference, yo), then you at least feel comfortable knowing that they got a roof over their heads and some stability.
Look... I just want Isaac back. Period. The fact some demoted ATs got trophies in the last installment but Isaac disappeared altogether was a slap in the face. If he's revealed as an Assist Trophy, there would be disappointment, but eventually, you'd get over with. Besides, we might get multiple trophies this time.
But, at this point of the franchise's existence, you feel like the potential is still there. The unfortunate reality of supporting a character like Isaac is they delay the inevitable until the very end, when you just want it over with so you can either move on or prepare for December. This unknown feeling affects you psychologically and makes you assume extremes as opposed to all potential options.